Re: infuriating Series[] question
- To: mathgroup at smc.vnet.net
- Subject: [mg17321] Re: infuriating Series[] question
- From: Dr Dan <drdanw at my-dejanews.com>
- Date: Fri, 30 Apr 1999 23:22:39 -0400
- Organization: Deja News - The Leader in Internet Discussion
- References: <7g0spa$dvc@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <7g0spa$dvc at smc.vnet.net>,
Peter Jay Salzman <psalzman at landau.ucdavis.edu> wrote:
> Dear all,
>
> I'm trying to develop very high order difference equations, and want to use
> Mathematica to save me from calculating tons of quantities like 5^10 / 7!
>
> If I define:
> g[x_] := Series[ f[x], {x,0,10} ]
>
> And try to compute stuff like:
>
> g[5*h] or g[10*h]
>
> It gives me the right answer, but i get terms like
>
> f'''''[0] * (5 x)^(10) / 10!
>
> The whole point in using Mathematica is so that I don't have to calculate
things
> which look like 5^10 / 10! (that's factorial, of course, not me being
> emphatic).
>
> Even when I try things like // Simplify or // FullSimplify, Mathematica
refuses to
> simplify these rational coefficients. One thing I've learned is that
Mathematica
> can do anything -- but figuring out how to do the something is often
> completely not obvious to a nominal user like me.
>
> Can someone tell me the secret here?
>
> Pete
Mathematica will always return an exact answer if possible. If you are
looking for a number, try using N (as in N[Series[...]] or //N) to convert
the exact expressions to approximate real numbers. Another trick is to use a
decimal point in the function, as in g[5.*h].
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